A series of spaced-apart optical amplifiers are typically in the transmission path of optical communications system to amplify optical signals that are being transported over the path. In such systems, a plurality of information bearing optical signals are typically transported over the optical path as multiplexed channels of different wavelengths. It has been noted that if the gain of an optical amplifier is different for the different channels being amplified, then the difference in gain accumulates as the signal channels pass through each of the series of amplifiers. Consequently, this results in the channels having different signal power levels and different signal to noise ratios, which undoubtedly impairs the performance of the optical communications system.
Disadvantageously, in a so-called point-to-point optical transmission system, such differences impose a severe limitation on the number of amplifiers that may be disposed in the transmission path before transmission quality of the weak channels becomes unacceptable. Consequently, this limits the transmission distance in a point-to-point transmission system. Further, in optical networks where signal channels from different transmission routes are branched or cross-connected, such differences limits the size and scale of the network.